Unless otherwise indicated herein, the materials described in this section are not prior art to the claims and are not admitted to be prior art by inclusion in this section.
A bellcrank is a device that is used to change the direction of movement and/or impart a mechanical advantage in a system. In an example, a bellcrank is used to change rotary motion to linear motion. Generally, a bellcrank may be used in any mechanical system where it is desired to change motion from one direction to another. Bellcranks are thus common in a variety of industries, including but not limited to the aerospace industry, the automotive industry, the construction industry, and the agricultural industry.
As a particular example, bellcranks are commonly used in the aerospace industry for systems that modulate fan flow in a turbofan engine by varying the exit or throat area of a nozzle at the trailing edge of a fan duct or thrust reverser sleeve. Such systems will be referred to herein as variable area fan nozzles (VAFNs). In particular, bellcranks are commonly used in VAFNs for turbofan engine nacelles so as to control the amount of opening and the rate at which the fan nozzle throat area changes. In an example VAFN, the VAFN includes an array of elastically deformable petals attached to a lip area at the downstream end of a thrust reverser sleeve. In other examples, pivotable rigid petals can be substituted for elastically deformable petals. In either case, petal deflection can be actuated using one or more flexible push-pull shafts (e.g., cables) which extend around a major portion of the fan nozzle circumference. An actuation system controls the deformation or deflection of the petals, thereby controlling the amount of opening and the rate at which the fan nozzle throat area changes. Alternatively, the cables can be replaced with rods, tubes or bands made of composite material.
VAFNs commonly include one or more bellcranks that actuate the flexible push-pull shafts. However, the typical VAFN bellcrank that actuates a flexible push-pull shaft has a number of drawbacks. For instance, one issue is that existing bellcrank arrangements impart side loading on the flexible shaft. The flexible shaft may be unsupported at the rod end. Since the flexible shaft is unsupported at the rod end, the flexible shaft is subject to side-loading due to the rotating motion of the bellcrank about its pivot point which moves the flexible shaft along a corresponding arc. Side loads may impact the functionality of the flexible shaft. For instance, side loads may lead to fatigue on the flexible shaft.
An existing solution for reducing or preventing side load on the flexible shaft is to incorporate a crank-slider or a cam mechanism in the bellcrank system. However, a drawback of this approach is that the crank slider or cam mechanism is external to the bellcrank, and an external crank slider or cam mechanism thus increases the size of the mechanical system. Since there is limited area within the VAFN, this increased size is undesirable. Further, another drawback of this approach is that the additional crank-slider or cam components and hardware that are used to secure the parts to the bellcrank mechanical system add considerable weight to the system.